Extruded closure strip carrying reactivatable adhesive layer

ABSTRACT

A closure strip adapted to be bonded to a substrate comprises a one-piece polymeric extrusion having a base surface essentially no wider than the profile portion of the strip and wherein a plane projected normal to and bisecting the base surface longitudinally into two parts also bisects the profile portion into two corresponding parts, a dormant but reactivatable adhesive layer adhering to and along the base surface on at least one side of the plane, so that the closure strip is adapted to be bonded to the substrate upon reactivation of the dormant adhesive.

BACKGROUND OF THE INVENTION

This invention relates to the art of synthetic plastic resin extrudedseparable fasteners and a method of making the same, and is moreparticularly concerned with prefabricating such fasteners at a high rateof production, economically and for subsequent union with desiredsubstrates.

As revealed in the prior art exemplified by U.S. patents, proposals foruniting extruded separable fasteners, sometimes referred to in the tradeas zippers, have comprised joining the fastener profile strips to acompatible extruded synthetic plastic film substrate while both of theseparately, but simultaneously extruded components are still in asufficiently plastic state to fuse together, as exemplified in U.S. Pat.Nos. 3,462,332 and 4,259,133.

Another technique, as exemplified in U.S. Pat. Nos. 3,784,432 and4,279,677, includes joining the freshly extruded profile strips tocompatible prefabricated plastic film substrate while the fastener stripis still in a sufficiently thermoplastic state to permit fusing thethermoplastic film which is reheated from a cold state to accelerate thefusion.

A further technique as exemplified in U.S. Pat. No. 3,532,571 includesjoining freshly extruded film to compatible prefabricated fastenerstrips while the film is still in a sufficiently thermoplastic state topermit fusing the fastener strip to the film.

It has, of course, been longtime common practice to join prefabricatedfastener strip to prefabricated compatible plastic film by fusionwelding, as exemplified in U.S. Pat. No. 3,948,705.

A distinct advantage attributable to prefabricating profile fastenerstrips and bag making plastic film resides in the fact that because ofthe relatively larger section modulus of the profile strips as comparedto the section modulus of the plastic film, the plastic film whenextruded separately can be run at a much greater speeds than the profilefastener strips. Therefore by spooling the prefabricated fastener stripsand the prefabricated film in separate rolls, they can be fedsimultaneously at desired speed and joined together as by means ofadhesive applied in a fluent state between the elements as they arebrought convergently together, as exemplified, by U.S. Pat. Nos.4,101,355; 4,341,575; 4,354,541 and 4,355,494. A distinct advantage ofsuch prefabrication and then adhesive joinder of the profile fastenerstrips and the substrate is that relatively incompatible materials maybe utilized to advantage in the respective elements. For example, a formof plastic material which will lend itself to best advantage forextrusion of the profile strips, and will afford the most advantageouselastic deformation separable coaction of the fastener profiles may beutilized for that purpose, while materials having specialcharacteristics desirable for the end product such as bags may beutilized in the film whether plastic or non-plastic. The compositefinished product will then be endowed with all of the preferredcharacteristic in both the fastener and the substrate.

With all of the advantages inherent in adhesively securing prefabricatedelastically deformable separable profile fastener strips toprefabricated film substrate, there is still room for substantialimprovement in the adhesive attachment technique. A disadvantage ofadhesive attachment as heretofore proposed has been the requirement forextremely accurate control of the fluent adhesive, both as to volume atpoint of application, temperature gradients during application,tackiness, machine down time, necessarily close attention to theadhesive applicators, avoidance of adhesive spray machine foul-up, andthe like. Therefore, onsite adhesive joinder of the profile fastenerstrips and the substrate has placed a heavy burden on the machineoperators to maintain all of the critical parameters necessary forsuccessful results. This has been particularly the case when theadhesive attachment is combined with a form fill operation as describedin U.S. Pat. No. 4,355,494, where the advantage of shipping finishedfilm and finished fastener separately and thereby saving space as wellas reducing spool change-over because of larger spools, are then lostdue to the relatively complex liquid adhesive applying operation.

It has been proposed in published U.K. Patent Application 2,080,412A toprovide fastener strips having sidewardly extending attachment webscarrying heat reactivatable adhesive. However, the fastener stripshaving such attachment webs are more costly to produce than a web-freefastener strip such as disclosed in British Pat. No. 1,587,609. Neitherof these British publications has an adequate teaching of how toprefabricate fastener strips with reactivatable adhesive, and inparticular such fastener strips without side attachment webs.

SUMMARY OF THE INVENTION

It is accordingly an important object of the present invention toovercome the disadvantages, drawbacks, inefficiencies, limitations,shortcomings, and problems inherent in prior extruded prefabricatedresiliently flexible fastener plastic profile strips, and to provide anew and improved fastener of this kind carrying reactivatable adhesivefor bonding the strips to a substrate.

To this end, the present invention provides a closure strip adapted tobe bonded to a substrate such as film in the manufacture of reclosablebags, the closure strip having a longitudinally extending base portionproviding a longitudinally extending base surface, and a profile portionextending longitudinally along the base portion and having profile meansprojecting in the opposite direction from that in which the base surfacefaces, the base and profile portions comprising an extrusion in onepiece from a polymeric material and being shaped cross-sectionally suchthat a plane projected normal to and bisecting said base surfacelongitudinally into two parts also bisects the profile portion into twocorresponding parts, and comprising said base surface being directlyback of said profile portion and of a width essentially no wider thansaid profile portion, and a dormant but reactivatable adhesive layeradhering to and along said base surface on at least one side of saidplane, so that the closure strip is adapted to be bonded to thesubstrate upon reactivation of the dormant adhesive.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will bereadily apparent from the following description of certainrepresentative embodiments thereof, taken in conjunction with theaccompanying drawing, although variations and modifications may beeffected without departing from the spirit and scope of the novelconcepts embodied in the disclosure, and in which:

FIG. 1 is an enlarged sectional elevational detail view showing asynthetic resin, resiliently flexible separable fastener comprising anassembly of complementary profile strips and provided with base surfaceadhesive pursuant to the present invention, by which the fastener isadapted to be secured to substrates;

FIG. 2 is a schematic perspective view demonstrating a preferred methodand apparatus for producing fasteners in accordance with the presentinvention.

FIG. 3 is an enlarged fragmentary sectional detail view takensubstantiallly along the line III--III of FIG. 2;

FIG. 4 is a schematic elevational view showing a modified mode ofapplying adhesive to the fastener strips;

FIG. 5 ia a view similar to FIG. 1, but showing a modification;

FIG. 5A is a view similar to FIG. 5 but showing a modification;

FIG. 5 is a view similar to FIG. 1 but showing another modified form ofthe resiliently flexible separable fastener pursuant to the presentinvention;

FIG. 7 is a schematic perspective view similar to FIG. 2 but showing amodification in the method and apparatus for producing the fastener ofFIG. 6;

FIG. 8 is an enlarged fragmentary sectional detail view takensubstantially along the line VIII--VIII of FIG. 7; and

FIG. 9 is a view similar to FIG. 4, but applicable to making thefastener of FIG. 6.

DETAILED DESCRIPTION

Referring to FIG. 1, an elastically deformable, resiliently flexibleseparable fastener 10 comprises preferably identical, extruded plasticstrips 11 of the plural interlocking rib and groove type. Each of thefastener strips 11 has a set of profiles 12 extending longitudinallyalong the strip, and which are of the separably interlocking hooked riband groove form. By way of example the profiles 12 provide complementarygrooves wherein the hooks of the rib profiles of the set on one of thefastener strips interengage within the complementary grooves of theprofile set on the companion or mating fastener strip.

Each of the fastener strips has a base surface 13 carrying a dormant butreactivatable adhesive 14 by which the base surface 13 is adapted to besecured to a substrate 15, such as film in the manufacture of reclosablebags, when the adhesive is reactivated, that is converted from agenerally non-sticky, dormant freely handleable state into a sticky,adherent operational state. It will be understood that the separablefastener 10, although shown for illustrative purposes in an enlargedform, may be produced in any desirable size suitable for the intendedpurpose, and in particular for making bag material.

As shown, the fastener strips 11 are advantageously free from lateralflanges, because according to the present invention such flanges areunnecessary. This not only saves plastic material, but also permits amuch greater rate of production of the plastic fastener strips 11carrying the profiles 12, because a greater number of the strips 11 canbe simultaneously extruded through an extrusion die. Because of the lackof lateral webs on the profile strips 11, the extrusion orifices can befairly closely spaced, and a greater multiple of fasteners can beextruded at one time. For example a fastener, or lock, adapted for smallbag making, and provided with side webs may require at least six timesas much space on the die per lock, as compared to a similar lock withoutwebs. Accordingly, a die can easily accommodate six times as manyweb-free locks without disturbance in the flow of plastic through theextruder, whereas to attempt to extrude the same number of locks whereinthe profile strips have attached webs would be extremely difficult tocontrol. This achieves significant production economy.

Another advantage of webless fastener profile strips is that 10,000' to15,000' storage and handling spools become readily available, whereasthe same size of profile strips with lateral webs must generally belimited to about 6,000' per spool, having regard to a spool size thatcan be readily handled. Spools with greater footage of fastener profilestrip require fewer changes in a production run where the strip isjoined to the substrate, and hence less spool change down-time is lostin production.

By way of emphasizing the particular construction and relationship ofthe elements of each of the closure or fastener strips 11, it may benoted that each base portion and more particularly the base surface 13of each strip 11 is located in alignment directly back of the profileportion of each strip, the profile portion projecting in the oppositedirection from that in which the base surface of the strip faces. Thebase portions and the profiles are extruded in one piece from apolymeric material and the strip in each instance is shapedcross-sectionally such that a plane P normal to and longitudinallybisecting the base surface 13 also bisects the profile portion into twoparts. The dormant but reactivatable adhesive 14 adhering to the basesurface 13 may be on both portions of the base surface 13 bisected bythe plane P, or may be located on the base surface 13 only along oneside of the plane P. The width of the base surface at either side of theplane P may be varied to suit many particular circumstances, especiallywhere the reactivatable adhesive 14 is to be carried by the surface 13but only on one side of the plane P.

As exemplified in FIG. 2, a compact four orifice extrusion die 18,having two sets of profile strip orifices 19, is thereby adapted toproduce simultaneously two complete fastener assemblies 10. Preferredthermoplastic materials from which the profile strips are adapted to beextruded comprise polyethylene having a melting point of from 230° F. to270° F., polypropylene having a melting point on the order of 345° F.,and the like.

According to the present invention, the adhesive 14 is adapted to beapplied to the fastener strip base surfaces 13 during extrusion of thestrips 11. In one useful mode the adhesive 14 comprises a so-called hotmelt adhesive selected from ethylene vinyl acetate, ethylene acrylicacid, polymer rubber resin blend, and the like, having a selectedbonding fusion range of from 175° F. to 260° F. The bonding fusiontemperature of the adhesive should be sufficiently less than the meltingpoint of the fastener profile strip material to which it is applied topermit the reaching of bonding fusion of the adhesive 14 from a coldgenerally dormant condition, by application thereto of heat at atemperature which will not cause softening deformation or any otherdeterioration of the plastic material of the fastener profile strip.

In another useful mode, the adhesive 14 may be of a type which after ithas been applied to the fastener strip base 13 is adapted to set to adry dormant, inactive state from which it can be reactivated by applyinga suitable quick acting solvent to its substrate-engageable surface justbefore the fastener strip joins a substrate to which it is adhesivelysecured by the reactivated adhesive.

Conveniently, application of the adhesive 14 to the base surfaces 13 ofthe profile strips 11 is adapted to be effected at the orifices 19, andin a useful mode by coextrusion through the orifices 19 in the die 18,as best visualized in FIGS. 2 and 3. For this purpose, the adhesive 14in a fluent state is supplied from a supply source 20 for each of theprofiles strips 11. From the supply source 20 the fluid adhesive isconducted through a passage 21 in each instance to that area of each ofthe die orifices 19 which shapes the respective base surface 13 of theprofile strip 11. As all of the plurality of profile strips 11 aresimultaneously extruded, the adhesive 14 that is applied as a layer tothe respective profile strip base surfaces 13 is carried along on thesurfaces 13 as the extruded strips emerges from the die 18.

Thence, the strips 11 carrying the adhesive thereon pass to and throughmeans defining a curing zone in this instance comprising a chillingchamber 22 (FIG. 2). There the profile strips 11 are firmed and set, andthe adhesive layers 14 are concurrently with the curing of the stripsset and cured to a dormant state on the base surfaces 13 but from whichdormant state the adhesive can be reactivated later on for bonding tothe substrates 15.

In the compact arrangement of FIG. 2, all of the orifices 19 areoriented to form the back surfaces 13 in a common plane, that is facingtoward the delivery ports or orifices of the adhesive delivery passages21. Thus the profiles 12 of the extruded strips 11 all face in theopposite direction. As shown all of the back surfaces 13 of all of thefastener strips 11 face upwardly and all of the profile ribs and grooves12 face downwardly. By preference the profiled fastener strips 11 areextruded in adjacent pairs so that downstream from the extrusionorifices 19, and after leaving the curing chamber 22, the pairs ofcomplementary strips 11 can be assembled together by relativelyreorienting the pairs of fastener strip and interengaging the profiles12. For example, means may be provided for twisting the corunningprofile strips 90° toward one another so that the profiles 12 face eachother, and then pushing the strips toward one another to interengage theprofiles. On the other hand, one of the profile strips may be twisted180° relative to the companion profile strip and then the strips joinedby pressing the companion strips together for interengaging the profiles12. For the latter maneuver, strip deflecting and twisting meansdesirably comprises a series of cooperatively related pairs of rollerscomprising a first pair of rotary pinch rolls 23, one of which engagesthe cured adhesive-carrying back surface 13 of one of the fastenerstrips 11 and the other of which engages the tips of the profile ribs12. That initiates not only a twisting of the engaged strip but alsodeflection of the strip toward the profiles 12 of the companion strip.Thereafter, one or more second pairs of pinch rolls 24, which may engagethe sides of the strip 11 being twisted and deflected, complete theturning of the strip into an inverted orientation with the profiles 12of the inverted strip aligned for interengagement with the profiles 12of the companion strip which has remained in the orientation in which itwas extruded while corunning with the deflected and twistinglyreoriented strip. Immediately downstream from this reorientation of thestrips 11, the companion strips are pressed together as by means ofpinch rolls 25 into closed fastener assembly relation. Downstream fromthe interlocked joining of the fastener strips into closed fastenerrelation, the continuously running fastener assemblies are adapted to bewound into storage rolls 27 of suitable size for subsequent handling andprocessing.

Any suitable driving means 26 may drive the pinch rolls 23, 24 and 25and the spooling means for the storage rolls 27, in properly coordinatedrelation.

If preferred, the adhesive layers 14 may be applied to the base surfaces13 of the fastener profile strips 11 during extrusion of the strips, butimmediately downstream from the extrusion die 18' (FIG. 4) by applyingthe adhesive through respective nozzles 28 communicating with adhesivesource 20' through passage means 21'. In this arrangement, similarly asin the arrangement where the adhesive 14 and the strips 11 arecoextruded, the adhesive and the profile strips are concurrently setinto cured condition, and then assembled similarly as has already beendescribed. Application of the adhesive by means of the nozzles 28 isalso well suited for applying an adhesive which is reactivatable bymeans of a solvent where the adhesive when applied is in a fluent stateby reason of a solvent vehicle so that the extruded heat of the fastenerstrips to which it is applied will accelerate driving off the solventfrom the adhesive with the curing of the adhesive and the fastenerstrips then completed concurrently.

Inadvertent, unintended adherence to any surface other than a chosensubstrate may sometimes occur by reason of the adhesive 14 possiblyhaving some latent tackiness for any reason after the curing step, orpossibly tending to reactivate prematurely when subjected to inadvertentor careless adverse environmental handling or exposure. To avoid suchoccurence, the arrangement disclosed in connection with FIG. 5 may beemployed, wherein the adhesive 14' is applied to the back surface 13' ofthe fastener strip 11' in each instance within a shallow channel definedon the back surface 13' between transversely spaced spacer and retainerribs 29 extending longitudinally and integral with the retainer strip11' and defining the opposite sides of the adhesive receiving channel.The ribs 29 are only slightly, if any, higher than the layer of adhesive14'.

At least two functions are attributable to the ribs 29. In one functionthe ribs 29 serve as spacers to maintain out of unintended adheringcontact with the adhesive 14' any object at least as wide as the strips11, such for example as the back of the companion fastener strip in thefastener assembly 10 rolled thereon in a storage spool, or storage orshipping packing material, or guide surfaces with which the strip mayhave to be in contact in an assembly operation with substrate. Toenhance the effectiveness of the spacer ribs 29, the base surface 13'may be formed slightly concave in transverse direction and the layer ofadhesive 14' applied to the concave base surface within the channel to asubstantially uniformed depth, so that the surface of the set adhesive14' will also be transversely concave conforming to the channel basesurface. Thereby the adhesive 14' will be maintained out of contact withthe surface of any object bridging across the spacers 29. However, byreason of the shallow depth of the adhesive containing channel and theshallow height of the ribs 29, only normally moderate relative assemblypressure between the fastener assembly back surfaces and substrate 15'with the adhesive 14' reactivated, will result in thorough adhesion ofthe fastener strips to the substrate. Where the material of the fastenerstrips 11' is of sufficient elasticity, pressing against the substrate15' in the bonding operation will cause uniform deflection of the basesurface 13' toward the substrate for bonding by the adhesive 14'. Wherethe material of the fastener strips 11 is relatively stiff, it may bedesirable to yieldably deform the substrate 15', such as a bag makingfilm or the like into the shallow adhesive containing channel providedby the back surface 13' between the spacers 29. Because of the shallownature of the channel and the spacers 29 deformation of the bondedsubstrate 15' may be hardly perceptible, and if perceptibleunobjectionable for most purposes.

Another function of the spacers 29 is to confine the adhesive 14'against spreading beyond the side edges of the fastener strips 11'. Thisavoids a possibly unsightly dross condition alongside the bond jointshould there be any tendency for the adhesive 14' in reactivatedfluidized or tackified condition to spread laterally from the bond jointunder pressure during the bonding operation.

Where it is desired to provide the adhesive 14' only along alongitudinal area on a portion of the back or base surface 13', thearrangement shown in FIG. 5A may be utilized wherein one of the shallowrib spacers 29 extends longitudinally along one edge of the base surface13', while a second one of the spacers 29 extends longitudinally alongan intermediate line on the base surface 13'. For example, where it isdesired to have the reactivatable dormant adhesive 14' on only one halfof the surface 13', the intermediate spacer 29 may extend along asubstantially medium longitudinal line on the base surface.

On reference to FIG. 6, an elastically deformable, resiliently flexibleseparable fastener 30 is of the type comprising a male profile 31 and afemale profile 32 which are of the separably interlocking hooked rib andgroove form, shown, by way of example, as comprising a generallyarrowhead cross-section on the male profile 31 adapted to interhook witha complementary channeled formation of the female profile 32. Each ofthe profile strips 31 and 32 has opposite its interlocking profileformation a base surface, comprising a base surface 33 on and extendingalong the male profile 31, and a base surface 34 extending on and alongthe female profile 32. Each of the fastener base surfaces 33 and 34carries a reactivatable adhesive 35 by which the respective basesurfaces are adapted to be secured to substrate 37 when the adhesive 35is reactivated, that is converted from a generally non-sticky, dormant,freely handleable state into a sticky, adherent operational state. Itwill be understood that the fastener 30, although shown for illustrativepurposes in an enlarged form, may be produced in any desirable sizesuitable for the intended purpose, and in particular for making bagmaterial. As will be observed, the fastener profile strips 31 and 32 areadvantageously free from lateral flanges, for the advantageous reasonsheretofore described.

As exemplified in FIG. 7, an advantageous fastener strip prefabricationextrusion arrangement is adapted to have a multi-orifice extrusion die38 adapted for simultaneously extruding profile fastener strip for asmany as four fastener assemblies simultaneously. Thermoplastic materialis supplied under extrusion pressure to the die 38 by means of anassociated extruder 39 which may be of any preferred form adapted forthis purpose. Conveniently four companion pairs, comprising a total ofeight extrusion orifices will provide for four of the fastenerassemblies 30. For this purpose four male profile strip extrusionorifices 40 are located in the die 38 in alignment with four respectivefemale fastener strip forming orifices 41. As shown, the orifices 40 arevertically aligned in superjacent spaced relation to the orifices 41.

As shown in FIGS. 7 and 8, adhesive 35 is adapted to be applied to thefastener strip base surfaces 33 and 34 by supplying fluent adhesive froma supply source 43 through ducts or passages 44 which deliver theadhesive 35 in the proper volume and width to the respective basesurfaces 33 and 34. This coextrusion of the fastener strip plastic andadhesive is especially suitable for heat reactivatable adhesive.

If it is preferred to apply the adhesive layers 35 to the respectivebase surfaces 33 and 34 of the profile strips 31 and 32, respectively,during extrusion of the strips but immediately downstream from theextrusion die 38' (FIG. 9), the adhesive 35 is adapted to be appliedthrough respective nozzles 45 which communicate with the respectiveadhesive sources 43' through the passage means 44'. When thus applied,the adhesive 35 may be of either the hot melt type or solvent fluidizedtype. In either event, the adhesive and profile strips are thenconcurrently set and cured by running the same through a curing chamber47 which receives the adhesive equipped corunning fastener strips 31 and32 adjacently downstream from the extrusion die 38. After the curedfastener strips with the cured adhesive thereon leave the curing chamber47, the fastener strips in vertical alignment pass between pinch rolls48 which squeeze the fastener strips toward and into assembly with oneanother wherein the male and female profiles are separableinterconnected. Downstream from the fastener strip assembly pinch rolls48, the fastener assemblies 30 are wound into storage rolls 49 ofsuitable size for subsequent handling and processing. It will beunderstood that the pinch rolls 48 and the usual cores or spools onwhich the rolls 49 are wound are adapted to be driven in any suitablemanner for advancing the extruded profile strips from the extrusion die38 at a speed compatible with the extrusion speed.

In use, the adhesive-carrying profile strips of the fastener assemblies10 or 30, as the case may be, are adapted to be joined to the substrates15 or 37 by reactivating the dormant adhesive 14 or 35 at a propertemperature below the softening point of the plastic material of theassociated profile strips, as the adhesive carrying base surfaces arebeing pressed into adherence with and bonded to the substrate. Where theadhesive carried by the fastener strip bases is of the solventreactivatable type, the solvent may be applied in any suitable mannerssuch as by means of a suitable applicator, for example an applicatorroll immediately upstream from the point at which bonding is effected.

It will be understood that variations and modifications may be effectedwithout departing from the spirit and scope of the novel concepts ofthis invention.

I claim as my invention:
 1. A closure strip adapted to be bonded to asubstrate such as film in the manufacture of reclosable bags, theclosure strip having a longitudinally extending base portion providing alongitudinally extending base furface, and a profile portion extendinglongitudinally along the base portion and having profile meansprojecting in the opposite direction from that in which the base surfacefaces, the base and profile portions comprising an extrusion in onepiece from a polymeric material and being shaped cross-sectionally suchthat a plane projected normal to and bisecting said base surfacelongitudinally into two parts also bisects the profile portion into twocorresponding parts, and comprising:said base surface being directlyback of said profile portion and of a width essentially no wider thansaid profile portion; and a dormant but reactivatable adhesive layeradhering to and along said base surface on at least one side of saidplane, so that the closure strip is adapted to be bonded to thesubstrate upon reactivation of the dormant adhesive.
 2. A closure stripaccording to claim 1, wherein said strip comprises a material selectedfrom polyethylene and polypropylene, and said adhesive comprises amaterial selected from polymer rubber resin blend, ethylene acrylicacid, and ethylene vinyl acetate.
 3. A closure strip according to claim1, wherein said base portion surface has spaced longitudinal ribsdefining a channel therebetween and within which channel said dormantbut reactivatable adhesive is located.